You can keep other city's garbage or provide them with water for money.
Venice was one of the two Italian cities that monopolized trade with the far east.
You need to specify which two cities you are referring to if you want to make it possible to answer your question.
Cities in which country or region? There are hundreds or even thousands of cities which could reasonably be called ancient, and you can bet that most of them were on trade routes. Cities existed then, and still mostly do now, because they were centers for trade. Go pick any two old cities reasonably near each other, you can be sure they had a trade route between them (unless they had some barrier like impassible mountains in between).
They made both cities two important harbours for trade
People and ideas also end up being exchanged when distant cities trade products.
The two cities on the trade routes located on the Nile River are Cairo and Luxor. Cairo, the capital of Egypt, served as a major trade hub and cultural center, while Luxor, known for its ancient temples and monuments, was an important religious and administrative city in ancient times. Both cities played significant roles in facilitating trade and commerce along the Nile.
The two I know of for sure ar Manchester and Liverpool
Genoa and Venice
shared trade
Through shared trade
Two notable port cities in France are Marseille and Le Havre. Marseille, located on the Mediterranean coast, is the largest port in France and serves as a major hub for trade and tourism. Le Havre, situated on the Seine River estuary, is one of the country's main ports for container shipping and international trade. Both cities play significant roles in France's maritime economy.
When two distant cities trade, not only do products move, but also information and knowledge about the goods, such as quality, pricing, and demand. Additionally, financial transactions and currency exchange facilitate the trade. Lastly, cultural exchanges often accompany the movement of products, influencing consumer preferences and practices in both locations.